Extremely hard and scratch-resistant
Coated using ion-beam systems to keep the heat load on the glass as low as
possible
Highest homogeneity with Plane-parallel circular disks having both sides
optically polished
Features an infrared-reflective coating that prevents the penetration of heat
into the telescope tube
The blocking of IR (heat radiation) holds the D-ERF filter plane-parallel even
with longer observation times
Fine quality raw glass construction to cope with the stresses of solar use,
while ensuring fantastic images and crystal clear observing

Note: Never use any eyepiece filter for solar observation without
objective front filter